Kramer wrote the text of the papal bullSummis desiderantes which Pope Innocent VIII published in 1484. The bull acknowledges the existence of witches and explicitly empowers the inquisition to prosecute witches and sorcerers. This bull was incoroporated in Kramer's book Malleus Maleficarum (literally "The Hammer of Witches") which was first published in 1487 and became very influential in endorsing the fight against witches.

Kramer failed in his attempt to obtain endorsement for this work from the top theologians of the Inquisition at the Faculty of Cologne, and they condemned the book as recommending unethical and illegal procedures, as well as being inconsistent with Catholic doctrines of demonology.[4]

In 1495 he was summoned to Venice to give public lectures, which were very popular. In 1500 he was empowered to proceed against the Waldensians and Picards.

^"Institoris" is the Latin genitive case of "Institor" ("retailer"). It was a common practice in those times to take the genitive of the father's name for latinization, but this genitive was used as nominative in Latin texts ("Venerabilis & religiosus frater Henricus institoris"). In German texts this name was abridged to "Institor," according to the custom of omitting Latin endings in translations (cf. "Iuvenalis" – "Juvenal").